A23187 induces HIF-1α via activation of p42/p44 ERK. HepG2 cells were pretreated for 30 minutes with different kinase inhibitors U0126 (A), SB203580 (B), SP SP600125 (C), LY294002 (D), or KN93 (E), followed by the treatment with A23187 (5μM). Cells were further cultured under normoxia or hypoxia. Proteins were harvested after 4 hours for HIF-1α and after 15 minutes for the respective kinase blot and detected by Western blotting with antibodies against phospho-p44/42-ERK, phospho-p38, phospho-Jun, and phospho-Akt (see “Materials and methods”).